The present invention relates generally to purification apparatuses comprising an irradiation chamber for liquid purification. The present invention relates in particular to a liquid purification assembly, to a beverage dispenser comprising such a purification apparatus, and to a method for purifying a liquid.
One of the most essential tasks in purifying liquids such as water for drinking is disinfection, so as to ensure that any pathogenic microorganisms (e.g. bacteria, viruses, and protozoans) present in the water cannot cause illness in anyone who drinks it. It is known to perform this disinfection by the process of ultraviolet (UV) irradiation, where a volume of water being treated is bombarded with high-energy radiation in the form of UV light. The UV light damages the DNA and RNA of the pathogenic microorganisms, destroying their ability to reproduce and effectively neutralizing their ability to cause disease.
Since such systems use light to disinfect, their effectiveness is reduced on liquid which is not naturally clear or which has not been filtered to remove suspended solids. The scope of “purification,” for the purposes of this document, should thus be understood as encompassing the disinfection of liquid in which turbidity is minimal.
Traditional UV liquid purification systems have employed gas-discharge lamps as UV sources, in particular mercury-vapor lamps. Recently, it has become more and more common to employ ultraviolet light-emitting diodes (UV-LEDs) as a source of ultraviolet light for irradiation. UV-LEDs have numerous advantageous aspects which makes them appealing for use in an ultraviolet liquid purification system, notably their compact size, robustness, and lack of toxic components such as the mercury vapor found in conventional lamps. The solid-state nature of UV-LEDs also enables them to be switched on and off instantly, a further advantage relative to conventional gas-discharge lamps.
There are several examples in the prior art of UV-LEDs being employed to purify a liquid by ultraviolet irradiation. For example, the document CN 202175579 describes an irradiation device in which a single tube is spiraled around an array of UV-LEDs, allowing a continuous treatment of liquid. The document DE102005057875 discloses a device for sterilization of sewage in small sewage treatment and purification plant with sequencing batch reactor method. However, in the disclosed device the treated water is pushed out of the device by untreated water, causing possible hydrodynamic difficulties such as the creation of short cuts and stagnation zones, so that the disclosed device cannot guarantee that all the water flowing through it is actually fully purified.
In a general manner, to ensure an efficient purification of the treated liquid, said liquid has to be irradiated by ultraviolet for a sufficient time. The known small purifications apparatuses (e.g. used in drinkable water fountains) commonly comprise an irradiation chamber where the liquid flow continuously when liquid is drawn from the purification apparatus.
The volume of the irradiation chamber reduces the average velocity of the liquid flowing in the irradiation chamber, thus enhancing the residence time of the liquid in said chamber, and so the irradiation time.
Typical irradiation chambers have substantially the shape of a cylinder, closed at each end by a straight wall.
However, in such liquid purification apparatuses, the irradiation time, which is an important factor in liquid purification by ultraviolet light irradiation, depends on the flow rate of the liquid in the irradiation chamber.
Indeed, the irradiation time is equal to the residence time in the irradiation chamber (assuming that the UV-LEDs are switched on), which depends on the flow rate. In particular in small purification apparatuses, a low flow rate of the liquid and a large number of ultraviolet sources are required.
Moreover, the when a fluid flows in the irradiation chamber, dead volumes (i.e. parts of the chamber where the fluid stagnates) and short cuts (streamline going directly from the inlet to the outlet of the irradiation chamber without being slowed) may exist. Dead volumes and short cuts reduce the disinfection efficiency of the irradiation chamber. Finally, in the purification apparatuses known in the state of the art, cross-contamination between treated and untreated liquid may occur, as the treated liquid is pushed out of the irradiation chamber by untreated liquid.
It is therefore an objective of the present invention to provide a liquid purification assembly using ultraviolet irradiation that solves or reduces at least one of the above mentioned drawbacks.